The present invention relates to optical and laser spectroscopy and, in particular, laser induced fluorescence (LIF) spectroscopy which has recently been explored as a technique for medical diagnosis.
It is known that fluorescence spectroscopy can be used to diagnose the presence of atherosclerosis in human artery wall, emphasizing the use of empirically defined algorithms to determine tissue type from fluorescence spectra. For example, using 476 nm LIF spectroscopy, Kittrell et al., "Diagnosis of Fibrous Atherosclerosis Using Fluorescence", Applied Optics, 24, 2280 (1985), have demonstrated that such an empirical algorithm can be used to differentiate normal aorta and early atherosclerotic plaque in vitro. Fluorescence spectra of normal aorta and fibrous plaque were differentiated by the peak to valley ratio of the fluorescence intensity at 600 nm to the intensity at 580 nm.
Catheters employing optical fibers for the illumination, viewing and treatment of tissue are now used with sources of laser radiation for a variety of medical applications. Through the insertion of the catheter into a human artery or bodily cavity, laser radiation of a given wavelength can be used to illuminate tissue within the body such that the tissue fluoresces. Radiation generated by tissue fluorescence is then conveyed by one or more of the optical fibers to the proximal end of the catheter where it can be analyzed to yield information about the tissue under examination.